The present invention relates to a method of printing corrugated board sheets, and more particularly to a method of preventing ink for printing presses from increasing in viscosity and a printing press for use in practicing the method.
The flexographic printing method wherein an aqueous ink is used for printing corrugated board sheets has the advantage that the ink dries rapidly, permitting the sheet to be fed directly to the subsequent step such as stamping immediately after printing.
FIG. 9 is a side elevation of a conventional flexographic printing press, and FIG. 10 is a fragmentary perspective view of the same (see the specification of JP-A No. 5-200986/1993). An inking roll 1 and a squeeze roll 2 are in contact with each other, and an ink reservoir 11 in the form of a groove is formed between the two rolls 1, 2. Disposed under the inking roll 1 in contact therewith is a plate cylinder 9 provided with a printing plate 90. A support roll 91 is disposed under the plate cylinder 9. The inking roll 1 is movable toward or away from the plate cylinder 9. When the two rolls 1, 2 are rotated in ink squeezing directions (inward directions), the ink on the surface of the inking roll 1 is transferred to the printing plate (not shown) attached to the plate cylinder 9, printing a corrugated board sheet S fed to the nip between the plate cylinder 9 and the support roll 91.
With reference to FIG. 10, the ink is supplied from a container 96 placed on the floor to the ink reservoir 11 via a pump 97, supply pipe 94 and supply nozzle 4. The ink for use in flexographic printing presses readily dries and therefore becomes solidified due to a rise in viscosity unless incessantly held in circulation. Accordingly, the ink flowing out from the ends of the two rolls 1, 2 is received by ink pans 98, 98 and collected in the container 96 through a return pipe 95 for continuously circulating the ink during printing. The return pipe 95 and the supply pipe 94 are over 8 m in length.
The ink invariably partly remains in the return pipe 95 and the supply pipe 94 without being fully collected in the event of a change of ink, for example, for a color change. The remaining portion of ink is washed away and discarded during cleaning. Further because the path of circulation of the ink is long, a large amount of liquid waste is produced by cleaning the path, consequently necessitating great equipment for treating the liquid waste. This entails the problem that the liquid waste treatment requires great initial cost and running cost.
FIG. 8 shows a printing press comprising a closed box 3 which is slidable along an ink reservoir 11 and which has incorporated therein a removable ink tank 31 and is provided with an ink supply nozzle 4 (see U.S. Pat. No. 5,697,299).
An object of the present invention is to provide a printing method wherein a flexographic ink is used and yet which does not require a long circulation path, prevents the ink from increasing in viscosity, diminishes the waste of ink in the event of a change of ink and does not necessitate any great equipment for the treatment of cleaning liquid waste, and more particularly to provide a method of preventing ink from increasing in viscosity and a printing press for use in practicing the method.
The present invention provides a method of printing by a printing press wherein an ink is supplied from an ink supply-aspiration nozzle 4 to an ink reservoir 11 provided between an inking roll 1 and a squeeze roll 2 pressed into contact with the inking roll 1, and the ink is transferred from the inking roll 1 to a printing plate attached to a plate cylinder 9 by the rotation of the inking roll 1, the ink supply-aspiration nozzle 4 being connected to a closed box 3 housing an ink tank 31 therein, the closed box 3 and the ink supply-aspiration nozzle 4 being movable along the ink reservoir 11. The printing method is practiced by repeatedly performing the steps of:
supplying the ink from the supply-aspiration nozzle 4 to the ink reservoir 11 at a location above the ink reservoir 11, i.e., at a midportion thereof,
moving the supply-aspiration nozzle 4 from the location along the ink reservoir 11, thereafter halting the nozzle 4 and causing the nozzle 4 to aspirate a predetermined amount of ink from the ink reservoir 11 to place the aspirated ink into the ink tank 31 within the closed box 3 and produce a flow of ink in the ink reservoir 11,
further moving the supply-aspiration nozzle 4 from the halted location along the ink reservoir 11 and causing the nozzle 4 to aspirate a predetermined amount of ink from the reservoir 11 to place the aspirated ink into the ink tank in the closed box 3 and produce a flow of ink in the ink reservoir 11.
A diluting liquid is supplied to the ink reservoir 11 while performing the above steps.
After supplying the ink, the supply-aspiration nozzle 4 is moved first toward one end of the ink reservoir 11, and subsequently toward the other end of the reservoir 11.
When the nozzle 4 aspirates the ink from one end portion of the ink reservoir 11 and places the ink into the ink tank 31 within the closed box 3, the liquid level of the ink lowers at the end portion, permitting the ink to flow toward the end portion. Since like step is also performed at the other end portion of the reservoir 11, the ink similarly moves along the reservoir 11 toward the other end portion. Ink is then supplied to the reservoir at a location away from the two end portions. A flow of ink also occurs at this time.
Since the above cycle is repeated during the printing operation, the ink incessantly flows in the ink reservoir 11, which is continuously stirred, whereby the ink is prevented from increasing in viscosity. Especially because the ink flows between the opposite end portions of the ink reservoir 11, the ink moves over an increased distance and is stirred effectively. The diluting liquid supplied for replenishment is thoroughly mixed with the ink owing to the stirring effect produced by the flow of ink.
The ink supply-aspiration nozzle 4 is slidable with the closed box 3 removably housing the ink tank 31 therein, so that the pipe channel between the nozzle 4 and the closed box 3 can be shortened. This prevents the ink from increasing in viscosity without necessitating a long circulation path conventionally required, consequently greatly diminishing the waste of ink to be involved in changing the ink and permitting liquid waste treatment at a much lower cost than conventionally.